Ball spline assembly

ABSTRACT

A sleeve and a splined shaft are coupled for rotation in unison and for relative linear movement by trains of anti-friction balls which circulate in pairs of load and return grooves circumferentially spaced from one another around the sized surface of the sleeve. The return grooves are size to receive the balls with free running clearance, and the balls are always in an unloaded or free return condition while traveling in the return grooves, the same grooves serving as return grooves at all times regardless of the direction of rotation of either the sleeve or the shaft. The load grooves are smaller than the return grooves, and the balls in alternate ones of the load grooves are loaded and transmit torque in one direction of rotation while the balls in the other load grooves are loaded and transmit torque in the opposite direction of rotation. If desired, the balls may be sized to fit between the load grooves and the shaft with zero clearance to establish an anti-backlash fit between the shaft and the sleeve. Also, the sleeve may be preloaded on the shaft simply by using balls sufficiently large to be deformed plastically between the load grooves and the shaft.

United States Patent Doran et al.

[451 July 4, 1972 [54] BALL SPLINE ASSEMBLY [72] Inventors: Leo F.Doran, Clawson; Theodore R.

Schlenker, Troy, both of Mich.

Beaver Precision Products, Inc., Troy, Mich.

[22] Filed: Sept. 23, 1970 [21] Appl.No.: 74,691

[73] Assignee:

Primary Examiner-Edward G. Favors AttarneyWolfe, Hubbard, Leydig, Voit &Osann, Ltd.

[5 7] ABSTRACT A sleeve and a splined shaft are coupled for rotation inunison and for relative linear movement by trains of anti-friction ballswhich circulate in pairs of load and return grooves circumferentiallyspaced from one another around the sized surface of the sleeve. Thereturn grooves are size to receive the balls with free runningclearance, and the balls are always in an unloaded or free returncondition while traveling in the return grooves, the same groovesserving as return grooves at all times regardless of the direction ofrotation of either the sleeve or the shaft. The load grooves are smallerthan the return grooves, and the balls in alternate ones of the loadgrooves are loaded and transmit torque in one direction of rotationwhile the balls in the other load grooves are loaded and transmit torquein the opposite direction of rotation. if desired, the balls may besized to fit between the load grooves and the shaft with zero clearanceto establish an anti-backlash fit between the shaft and the sleeve.Also, the sleeve may be preloaded on the shaft simply by using ballssufficiently large to be deformed plastically between the load groovesand the shaft.

7 Claims, 3 Drawing Figures BALL SPLINE ASSEMBLY BACKGROUND OF THEINVENTION This invention relates to a ball spline assembly and, moreparticularly, to an assembly comprising inner and outer telescopedmembers which are coupled together for rotation in unison and for linearmovement relative to one another by one or more trains of anti-frictionbearing balls interposed between the two members and adapted tocirculate within load and return runs. The load runs are defined in partby grooves located between the members and formed in one of the members,the balls being received in the grooves and engaging radially projectingribs on the other member to transmit torque between the members. Inorder to reduce the outside diameter of the overall assembly and toprovide a more compact assembly, certain prior assemblies have beendesigned with internal return runs, that is to say, the return runs aredefined by grooves which also are located between the two telescopedmembers rather than by grooves spaced radially from the load grooves.Prior assemblies of this general type are disclosed in-U.S. Pat. Nos.1,918,108; 2,791,894; 2,908,152 and 3,304,745.

SUMMARY OF THE INVENTION The primary aim of the present invention is toprovide a new and improved ball spline assembly which is of compactconstruction with internal return grooves but which optionally may beeasily manufactured in such a manner as to maintain the balls in theload grooves in a tight anti-backlash or even a preloaded conditionbetween the load grooves and the torque transmitting ribs whilemaintaining the balls in the return grooves in an unloaded condition atall times.

A more detailed object is to accomplish the foregoing through theprovision of a novel ball spline assembly with internal return grooveswhich always maintain the balls therein in an unloaded condition andserve only as return grooves regardless of the direction of rotation ofeither of the telescoped members. In addition, the load grooves of theassembly serve only as load grooves and the balls may be selectivelysized to fit therein and against the ribs with an anti-backlash fit orin a preloaded condition with the balls in alternate ones of the loadgrooves being loaded and transmitting torque when one of the members isrotated in one direction and with the balls in the other load groovesbeing loaded when such member is rotated in the opposite direction.

The invention also resides in the unique difference between the sizingof the load and return grooves and in the novel positioning of thegrooves relative to the ribs to enable the balls to be sized to couplethe members with an anti-backlash fit while allowing substantially freereturn of the balls in an unloaded condition.

These and other objects and advantages of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary side elevationof a new and improved ball spline assembly embodying the novel featuresof the present invention, parts being broken away and shown in section.

FIG. 2 is an enlarged cross section taken along the line 2--2 of FIG. 1.

FIG. 3 is a fragmentary cross section, on a reduced scale, takensubstantially along the line 3-3 of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in thedrawings for purposes of illustration, the invention is embodied in aball spline assembly including an outer member or sleeve 11 telescopedover an inner member in the form of a splined shaft 13 and capable ofbeing moved linearly relative to the shaft while being rotatable inunison with the shaft. The sleeve, for example, may be anchored to arotary member (not shown) which turns with the sleeve as the shaft isrotated and which is shifted along the shaft with the sleeve.Alternatively, the sleeve may be rotated to turn the shaft and may beheld in an axially fixed position while the shaft is advanced throughthe sleeve.

In this particular instance, the shaft 13 is formed with sixcircumferentially spaced and axially extending channels 14 (FIG. 2)which alternate with six radially projecting ribs 15 designated as 15gand 151 in the drawings. Formed around and extending along the innerside of the sleeve 1 l are six circumferentially spaced pairs ofcircumferentially spaced grooves 16 and 17 which open toward the shaft,the grooves 16 having been designated as 16a and 16b in the drawings.The grooves of each pair are separated by comparatively wide lands l9projecting inwardly from the sleeve while adjacent pairs of grooves areseparated by narrower inwardly projecting lands 20. Each pair of groovesis disposed between adjacent ones of I the ribs 15 and each pair isassociated with one of the channels 14, the grooves being spacedradially outwardly from the channels.

An endless train of spherical anti-friction balls 21 is captivatedwithin each pair of grooves 16 and 17 and the associated channel 14 tocirculate axially therealong as the sleeve 11 is moved relative to theshaft 13 so as to reduce friction between the sleeve and the shaft.Also, the balls engage certain ones of the lands 19 and 20 and the ribs15 as they circulate and serve to transmit torque between the shaft andthe sleeve as one or the other is rotated. In circulating from thegrooves 16 to the grooves 17, or vice versa, the trains of balls 21 rollaround the ends of the lands 19 and transversely across the channels 14in the shaft 13. The balls are retained in the sleeve by end caps 23(FIGS. 1 and 3) suitably secured to each end of the sleeve and eachformed with six circumferentially spaced pockets 24 of semi-circularcross section positioned opposite the ends of the pairs of grooves.Thus, the balls roll chordwise and circular fashion across the shaft andinto the pockets 24 as they circulate between one groove of a pair andthe other groove of the pair.

As a result of the arrangement of the circumferentially spaced grooves16 and 17 and the end caps 23 with the chordally extending pockets 24,the circuit for each train of balls 21 is internal, that is, thecircuits for the most part are located between the sleeve 11 and theshaft 13 so that the overall diameter of the spline assembly 10 for ashaft of a given size can be made small as compared to those types ofassemblies in which the balls circulate radially between a load groovelocated between the shaft and the sleeve and a return groove spacedradially outwardly from the load groove. An assembly of the latter typeis disclosed in Sears US. Pat. No. 2,945,366.

In accordance with the present invention, the ball spline assembly 10,while being comparatively compact as a result of having internalcircuits for the balls 21, is arranged in a novel manner so that, ifdesired, the manufacturer of the assembly may easily construct theassembly such that the balls establish a tight anti-backlash fit betweenthe sleeve 11 and the shaft 13 and thereby prevent rotational play orlost motion between the two at all times. The balls are, however, alwaysleft free to recirculate with little restraint so as to avoid impedinglinear movement of the sleeve relative to the shaft.

To achieve the foregoing, the grooves 16 serve only as load grooves andare sized to receive the balls 21 with less clearance than the grooves17. When the shaft 13, for example, is rotated clockwise, the balls inalternate ones of the load grooves (i.e., the grooves 16a) are loadedfully and transmit the torque from the ribs 15 to the sleeve 11. Theballs in the remaining load grooves 16b simply circulate idly or underreduced load and do not transmit torque. When the shaft is rotatedcounterclockwise, however, the balls 21 in the grooves 16b are loadedfully and transmit torque while the balls in the grooves circulate idlyor under reduced load. At the option of the manufacturer of the assembly10, the balls may be sized to fit into the load grooves 16a and 16b andagainst the ribs 15 with zero clearance to establish an anti-backlashfit between the shaft and the sleeve. The grooves 17, however, arealways sized to receive the balls with greater clearance than the loadgrooves and simply serve to return the balls to the load grooves at alltimes regardless of the direction of rotation of either the shaft or thesleeve. As a result, the balls are always unloaded or under reduced loadwhen traveling in the return grooves 17 and circulate comparativelyfreely therein to enable the balls in the load grooves 16a and 16b totravel without impeding relative linear movement between the shaft andthe sleeve.

More specifically, the load grooves 16a and 16b of each adjacent pair ofgrooves are disposed adjacent one another and on opposite sides of theintervening rib 15. The load grooves 16a and 16b are of semi-circularcross section and coact with the sides of the intervening ribs to defineload runs for the balls, such ribs being radiused along their sides asindicated at 25 in FIG. 2. In this particular instance, the assembly isof the anti-backlash type and thus the balls 21 selected for use withthe assembly are sized relative to the load grooves so as to fit tightlybetween the grooves and the sides of the ribs with substantially zeroclearance to establish an anti-backlash fit between the sleeve 1 1 andthe shaft 13.

The return grooves 17 of adjacent pairs of grooves are disposed adjacentone another on opposite sides of alternate ribs 15, the sides of suchribs also being radiused as indicated at 31 in FIG. 2. Each returngroove 17 also is of semi-circular cross section but is formed with agreater radius than the radii of the load grooves 16a and 16b. Thus, theballs fit rather loosely in the return grooves 17 and may circulatefreely within the return grooves and alongside the ribs disposed betweensuch grooves.

With the foregoing arrangement, only the three ribs disposed between theload grooves 16a and 16b serve as torque transmitting ribs and thusthese ribs have been designated by the reference numeral 151. If theshaft 13 is rotated clockwise or the sleeve 11 rotated counterclockwise,the balls in the load grooves 16a are loaded between the grooves and thesides of the ribs 15! to transmit torque between the shaft and thesleeve. The balls in the load grooves 16b are not placed under load andcirculate without transmitting torque. If the shaft 13 is rotatedcounterclockwise or the sleeve 11 rotated clockwise, the balls 21 in theload grooves 16b are loaded between the grooves and the sides of theribs 151 and transmit torque while the balls in the load grooves 16acirculate without transmitting torque. Because of the anti-backlash fitbetween the balls 21, the torque transmitting ribs 15! and the loadgrooves 16a and 16b, the angular position of the shaft l3'relative tothe sleeve 11 cannot substantially change and thus torque is transmittedbetween the two without any rotary play or lost motion.

Regardless of the direction of rotation of either the sleeve 11 or theshaft 13, the balls 21 in the larger return grooves 17 always remainunloaded and circulate freely in the grooves. The three ribs 15 disposedbetween the return grooves 17, being held in a fixed angular positionrelative to the grooves by the balls in the load grooves 16a and 16b,never transmit torque and function only to guide the balls as theycirculate. These guide ribs thus have been designated by the referencenumeral 15g. The actual positions of the balls relative to the guideribs 15g and the return grooves 17 will vary somewhat from the positionsshown in FIG. 2 depending upon the influences of gravity and centrifugalforce.

Another important advantage of the invention is that the balls 21 alsocan be actually placed in a preloaded condition in the load grooves topositively insure against the existence of any rotary play between thesleeve 11 and the shaft 13 even though the dimensions of the balls andthe grooves 160 and 16b fall near opposite extremes of permissibletolerance ranges. Preloading of the balls is accomplished simply byusing at least one train of balls whose minimum radii are sufficientlylarge that the balls will be plastically deformed to a slight extent asthe balls enter the load groove associated with the train. Thus, theballs will be under a slight load at all times while in the load groovesso as to avoid rotary play between the sleeve and the shaft and toenable the assembly 10 to transmit torque with minimum torsionaldeflection.

From the foregoing, it will be apparent that the present inventionbrings to the art a comparatively compact ball spline assembly 10 withinternal return grooves 17. While the balls can be fitted into the loadgrooves 16a, 16b with clearance as in a standard, non-precisionassembly, an anti-backlash or preloaded assembly may be provided simplyby selecting and using balls 21 of appropriate diameter. Thus, eitherstandard, anti-backlash or preloaded assemblies may be supplied from asingle inventory of identical sleeves 11 and shafts 13.

We claim as our invention:

1. In a ball spline assembly, the combination of, inner and outertelescoped members adapted for rotation in unison and for relativelinear movement, said inner member having a series of circumferentiallyspaced channels alternating with outwardly projecting ribs, said outermember having circumferentially spaced pairs of circumferentially spacedgrooves with the grooves of each pair associated with one of thechannels, a train of anti-friction balls captivated in each pair ofgrooves to circulatetherein and in the associated channel as an incidentto relative linear movement of said members, one groove of each pairdefining a return run sized to receive the balls with clearance toenable the balls to circulate comparatively freely therein at all timesregardless of the direction of rotation of either of said members, theother groove of each pair defining a load run sized to receive the ballswith less clearance than the return runs, the grooves of each pair beinglocated with the load run of such pair positioned next to the load runof one adjacent pair and with the return run of such pair positionednext to the return run of the other adjacent pair whereby the balls inalternate load runs are loaded and transmit torque between said memberswhen one of the members is turned in one direction and the balls in theremaining load runs are loaded and transmit torque between the memberswhen said one member is turned in the opposite direction and wherebysaid balls circulate comparatively freely in said return runs regardlessof the direction of rotation of said one member.

2. In a ball spline assembly, the combination of, inner and outertelescoped members, one of said members having a series ofcircumferentially spaced channels alternating with radially projectingribs, the other of said members having circumferentially spaced pairs ofcircumferentially spaced grooves with the grooves of each pair disposedbetween adjacent ribs and associated with one of said channels, a trainof anti-friction balls captivated to circulate in each pair of groovesand in the associated channel to transmit torque between the memberswhile permitting relative linear movement of the members, a first grooveof each pair being a load groove and warning with the side of theadjacent rib to define a load run sized to receive the balls tightlywith an anti-backlash fit regardless of the direction of rotation ofeither of said members, the second groove of each pair being a returngroove and coacting with the side of the adjacent rib to define a returnrun sized to receive the balls with clearance to enable the balls tocirculate comparatively freely regardless of the direction of rotationof either of said members, and the grooves of each pair being locatedwith the load groove of such pair positioned next to the load groove ofone adjacent pair and with the return groove such pair positioned nextto the return groove of the other adjacent pair.

3. A ball spline assembly as defined in claim 2 in which said balls arespherical and in which said grooves are of arcuate cross section, theradii of said return grooves being larger than the radii of said loadgrooves.

4. A ball spline assembly as defined in claim 3 in which the balls of atleast one of said trains are sized relative to the associated load runso as to be deformed plastically when traveling in such load run.

5. In a ball spline assembly, the combination of, first and secondtelescoped members, said first member having circumferentially spacedpairs of circumferentially spaced grooves opening toward said secondmember, a train of anti-friction balls captivated in each pair ofgrooves to circulate therein as an incident to relative linear movementof said members, said second member having a series of circumferentiallyspaced and radially projecting ribs extending between the balls inadjacent grooves of adjacent pairs, alternate ones of said ribs beingtorque transmitting ribs operable to couple the members together forrotation in unison and each coacting with the two adjacent grooves todefine load runs sized to receive the balls tightly with ananti-backlash fit regardless of the direction of rotation of either ofsaid members, the remaining ones of said ribs being guide ribs and eachcoacting with the two adjacent grooves to define return runs sized toreceive the balls with clearance to enable the balls to circulatecomparatively freely regardless of the direction of rotation of eitherof said membets.

6. In a ball spline assembly, the combination of, first and secondtelescoped members, said first member having an even number ofcircumferentially spaced sets of circumferentially spaced load andreturn grooves opening toward said second member, a train ofanti-friction balls captivated in each set of grooves to circulatetherein as an incident to relative linear movement of said members, saidsecond member having a series of circumferentially spaced and radiallyprojecting torque transmitting ribs engageable with the balls to couplesaid members together for rotation in unison, there being one-half asmany torque transmitting ribs as pairs of grooves with each torquetransmitting rib being disposed between the balls in the load grooves ofadjacent sets of grooves and coacting with the load grooves to defineload runs sized to receive the balls tightly with an anti-backlash fitregardless of the direction of rotation of either of said members, andsaid return grooves coacting with said second member to define returnruns sized to receive the balls with clearance to enable the balls tocirculate comparafively freely regardless of the direction of rotationof either of said members.

7. In a ball spline assembly, the combination of, first and secondtelescoped members, said first member having two circumferentiallyspaced sets of circumferentially spaced load and return grooves openingtoward said second member with the load grooves of the two sets beingdisposed adjacent one another, a train of anti-friction balls captivatedin each set of grooves, means connecting the ends of the load and returngrooves of each set to one another to enable the balls to circulate inthe grooves as an incident to relative linear movement of said members,said second member having a radially extending rib projecting betweenthe trains of balls in the two load grooves to couple the memberstogether for rotation in unison and coacting with the load grooves todefine load runs of a predetermined radii, and said return groovescoacting with said second member to define return runs of a greaterradii than said load runs to enable the balls to circulate comparativelyfreely regardless of the direction of rotation of either of saidmembers.

1. In a ball spline assembly, the combination of, inner and outertelescoped members adapted for rotation in unison and for relativelinear movement, said inner member having a series of circumferentiallyspaced channels alternating with outwardly projecting ribs, said outermember having circumferentially spaced pairs of circumferentially spacedgrooves with the grooves of each pair associated with one of thechannels, a train of anti-friction balls captivated in each pair ofgrooves to circulate therein and in the associated channel as anincident to relative linear movement of said members, one groove of eachpair defining a return run sized to receive the balls with clearance toenable the balls to circulate comparatively freely therein at all timesregardless of the direction of rotation of either of said members, theother groove of each pair defining a load run sized to receive the ballswith less clearance than the return runs, tHe grooves of each pair beinglocated with the load run of such pair positioned next to the load runof one adjacent pair and with the return run of such pair positionednext to the return run of the other adjacent pair whereby the balls inalternate load runs are loaded and transmit torque between said memberswhen one of the members is turned in one direction and the balls in theremaining load runs are loaded and transmit torque between the memberswhen said one member is turned in the opposite direction and wherebysaid balls circulate comparatively freely in said return runs regardlessof the direction of rotation of said one member.
 2. In a ball splineassembly, the combination of, inner and outer telescoped members, one ofsaid members having a series of circumferentially spaced channelsalternating with radially projecting ribs, the other of said membershaving circumferentially spaced pairs of circumferentially spacedgrooves with the grooves of each pair disposed between adjacent ribs andassociated with one of said channels, a train of anti-friction ballscaptivated to circulate in each pair of grooves and in the associatedchannel to transmit torque between the members while permitting relativelinear movement of the members, a first groove of each pair being a loadgroove and coacting with the side of the adjacent rib to define a loadrun sized to receive the balls tightly with an anti-backlash fitregardless of the direction of rotation of either of said members, thesecond groove of each pair being a return groove and coacting with theside of the adjacent rib to define a return run sized to receive theballs with clearance to enable the balls to circulate comparativelyfreely regardless of the direction of rotation of either of saidmembers, and the grooves of each pair being located with the load grooveof such pair positioned next to the load groove of one adjacent pair andwith the return groove such pair positioned next to the return groove ofthe other adjacent pair.
 3. A ball spline assembly as defined in claim 2in which said balls are spherical and in which said grooves are ofarcuate cross section, the radii of said return grooves being largerthan the radii of said load grooves.
 4. A ball spline assembly asdefined in claim 3 in which the balls of at least one of said trains aresized relative to the associated load run so as to be deformedplastically when traveling in such load run.
 5. In a ball splineassembly, the combination of, first and second telescoped members, saidfirst member having circumferentially spaced pairs of circumferentiallyspaced grooves opening toward said second member, a train ofanti-friction balls captivated in each pair of grooves to circulatetherein as an incident to relative linear movement of said members, saidsecond member having a series of circumferentially spaced and radiallyprojecting ribs extending between the balls in adjacent grooves ofadjacent pairs, alternate ones of said ribs being torque transmittingribs operable to couple the members together for rotation in unison andeach coacting with the two adjacent grooves to define load runs sized toreceive the balls tightly with an anti-backlash fit regardless of thedirection of rotation of either of said members, the remaining ones ofsaid ribs being guide ribs and each coacting with the two adjacentgrooves to define return runs sized to receive the balls with clearanceto enable the balls to circulate comparatively freely regardless of thedirection of rotation of either of said members.
 6. In a ball splineassembly, the combination of, first and second telescoped members, saidfirst member having an even number of circumferentially spaced sets ofcircumferentially spaced load and return grooves opening toward saidsecond member, a train of anti-friction balls captivated in each set ofgrooves to circulate therein as an incident to relative linear movementof said members, said second member having a series of circumferentiallyspaced and Radially projecting torque transmitting ribs engageable withthe balls to couple said members together for rotation in unison, therebeing one-half as many torque transmitting ribs as pairs of grooves witheach torque transmitting rib being disposed between the balls in theload grooves of adjacent sets of grooves and coacting with the loadgrooves to define load runs sized to receive the balls tightly with ananti-backlash fit regardless of the direction of rotation of either ofsaid members, and said return grooves coacting with said second memberto define return runs sized to receive the balls with clearance toenable the balls to circulate comparatively freely regardless of thedirection of rotation of either of said members.
 7. In a ball splineassembly, the combination of, first and second telescoped members, saidfirst member having two circumferentially spaced sets ofcircumferentially spaced load and return grooves opening toward saidsecond member with the load grooves of the two sets being disposedadjacent one another, a train of anti-friction balls captivated in eachset of grooves, means connecting the ends of the load and return groovesof each set to one another to enable the balls to circulate in thegrooves as an incident to relative linear movement of said members, saidsecond member having a radially extending rib projecting between thetrains of balls in the two load grooves to couple the members togetherfor rotation in unison and coacting with the load grooves to define loadruns of a predetermined radii, and said return grooves coacting withsaid second member to define return runs of a greater radii than saidload runs to enable the balls to circulate comparatively freelyregardless of the direction of rotation of either of said members.